There are at least five genetically distinct collagen types whose degradation may be controlled independently. The initial step of collagen degradation is performed by collagenase, which makes a single cut through the collagen triple helix. We and others have found that type IV basement membrane collagen is not degraded by human skin collagenase, suggesting that a separate collagenase may degrade type IV collagen. A collagenase which preferentially degrades type IV collagen has been derived from a metastasis of the T241 fibrosarcoma.